Before purchasing "nylon webbing" (as it's often called), be sure to measure the width. Purchase webbing that is the same width as the original webbing on the harness. Also be sure to measure the length. Perhaps ordering 30% more then you need will provide extra material for mistakes.

To record how to route the new nylon webbing through any buckles or couplings, take a picture of the section of harness that you wish to replace.